Method for preventing the formation of hydrates and ice

ABSTRACT

A method for preventing the formation of hydrates and ice in a gas by conditioning methanol and injecting said conditioned methanol into the gas conduit.

United States Patent 1 Feb. 22, 1972 Clark [54] METHOD FOR PREVENTING THE 2,105,435 1/ 1938 Tanner et al. ..48/ 190 UX FORMATION OF HYDRATES AND ICE 2,266,981 12/1941 Miller ..48/l90 3,331,214 7/1967 Proctor et a1... ..47/196 X [72] lnvenm Merh 1,006,324 10/1911 Werner 48/180 c ux [73] Assignee: Phillips Petroleum Company 1,915,971 6/1933 Beane et al. ..48/ 190 3,057,706 10/1962 Marshall, Jr. et a1. ..48/196 [22] 1970 337,408 3/1886 Kearns 48/190 ux [21] Appl. No.: 17,622 1,726,018 8/ 1929 Farm: .48/190 UX 2,693,351 11/1954 Riley et a1 ..48/190 X ..4 4 7 [52] Us CL 8,190 Pnmary Exanuner-Joseph Scovronek 511 1111. c1 ..Fl7d 1/04, F1711 1/05 HWY-Young and Qmgg [58] Field of Search ..48/190, 196; 260/676 H; 62/48;

137/3, 2 US, 1, 88, 98 ABSTRACT A method for preventing the formation of hydrates and ice in [56] Reem a gas by conditioning methanol and injecting said conditioned UNITED STATES PATENTS methanol into the gas conduit. 559,992 5/1896 Bueb ..48/190 4 Claims, 2 Drawing Figures J TREATED GAS RESIDUE GAS SEPARATOR 5 g 4 f -MM/wWv-/ww 5 SEPARATOR N Yv i I ll] 32 0 2e {21 ,1 A o #1 J 1 1a ;/M ETHANOL MAKE-UP GLYCOL WASH METHANOL RECONCENTRATION ZONE 1 3e WATER 1. HC

METHOD FOR PREVENTING THE FORMATION OF HYDRATES AND ICE This invention resides in a method for preventing the formation of hydrates and ice in a gas stream. In another aspect, this invention resides in a method for conditioning a volume of gas hydrate and ice inhibitor, such as methanol for example, and injecting said conditioned methanol for example into a gas stream for the prevention of gas hydrates and ice formation in said gas stream.

I-Ieretofore, in the prevention of hydrates and ice formation in a gas conduit, a gas hydrate and ice formation inhibitor, such as liquid methanol, was injected into said conduit. This method was only partially successful owing to the fact that the liquid methanol often did not become thoroughly mixed with the gas. Where hydrate and ice formation was prevented by the injection of liquid methanol, it has been found that excessive amounts of methanol were necessary owing to the abovestated problem of poor mixing one with the other. The operation therefore generally resulted in inadequate hydrate and ice prevention or the utilization of excessive amounts of materials, labor, and time. As known in the art, see Hydrate Formation in Natural Gas by D. I... Kalz, pages 90 through 93 of Natural Gasoline Supply Mens Association Technical Manual, 5th Edition, for the Natural Gasoline and Cycling Industries, of the Natural Gasoline Association of America, March 1946, gas hydrate and ice formation depends on gas composition, moisture content, pressure, and temperature.

It is therefore an object of this invention to provide an improved method for preventing the formation of hydrates and ice in a gas stream. Another object of this invention is to provide a method for conditioning a gas hydrate and ice formation inhibitor, hereafter referred to as methanol, and injecting said conditioned methanol into a gas stream for preventing the formation of hydrates and ice in said gas stream. Yet another object of this invention is an improved method for preventing the formation of hydrates and ice in a gas stream that is being chilled and in a gas stream that is being expanded. Other aspects, objects, and advantages of the present invention will become apparent from a study of the disclosure, the appended claims, and the drawing.

The drawings are diagrammatic views of a typical gas processing system in which the method of this invention can be utilized.

FIG. 1 shows the system and FIG. 2 shows one apparatus for injecting methanol into the gas stream. 7

Referring to FIG. 1, a gas stream is flowing through a gas conduit 2 and a heat-exchanger system 4. The methanol conduit 6 is attached to the gas conduit 2 in fluid communication therewith for injecting a volume or quantity of methanol into the gas conduit 2 and into contact with the gas stream contained therein. A heating element 8, such as an indirect steam heater, for example, is associated with the methanol conduit 6 for heating the methanol to a temperature sufficient to vaporize the methanol and maintain said methanol in a vapor phase during injection of said methanol into the gas conduit 2 and into contact with the gas contained therein. Since the formation of ice and hydrates in a gas stream is the greatest in areas of gas expansion and cooling, it is preferred that the methanol conduit 6 be connected to the gas conduit 2 at a position adjacent and upstream of a location at which said gas stream is chilled and/or expanded and subjected to conditions of gas hydrate formation. In order to further assure more complete mixing of the methanol vapor and gas stream, it is preferred that the methanol stream be divided into a plurality of heated streams and said streams injected into the gas conduit 2 at spaced-apart locations relative one to another. One method for dividing the stream into a plurality of streams is to cap the end of conduit 6 and perforate the portion of conduit 6 that is within conduit 2 as shown in FIG. 2.

In an example use of the method of this invention as shown in FIG. I, heated methanol is injected into the gas conduit 2 at a position upstream of a heat exchanger 4 where the gas stream is chilled prior to entering a demethanizer 10 by way of first and second separators 12,14. The methanol-containing fluid is recovered from the bottom of the demethanizer 10, passed countercurrently through a washing fluid 16, composed of glycol and a small percentage of water, and processed within a conventional methanol reconcentration unit 18 for the removal of carbon dioxide, water, and hydrocarbon from the methanol fluid by heat and fractionation. The reconcentrated fluid containing about 98 percent methanol is thereafter delivered by a pump 20 by the heating element 8 at which the temperature of the methanol is increased to a temperature sufficient to vaporize the methanol and maintain said methanol in the vapor phase at least until the methanol vapor has been thoroughly mixed with the gas. A conventional dewpoint analyzer 22 can be positioned upstream of the methanol injection location 24 for determining the relative amount of water vapor contained in the gas. A signal from the analyzer can then be utilized to regulate the proper volume of methanol vapor injected into the gas conduit 2. Other analyzers 26,28 can be associated with the system to further regulate the injection and conditioning of the methanol.

In the operation of the controlling system that regulates the rate of methanol injected into the gas stream, detection of a change in the water content of the gas stream by the dewpoint analyzer 22 causes a signal to be delivered along line 29 to a control valve 30 that is positioned within the conduit 6. That signal, which can be an electrical or a fluid signal, preferably an electrical signal for maintaining a decreased response time, causes the control valve 30 to move to a more open position when the water content of the gas increases and to a more closed position when the water content of the gas decreases. The control valve 30 can also be connected to a moisture analyzer 26 that detects moisture changes in the methanol and water stream discharging from the first separator 12. A change in the water content of the water-methanol stream discharging from the first separator 12 through line 32 causes a signal to be delivered along line 34 to the control valve 30. An increase in water content of the stream flowing through line 32 indicates a greater water content in the gas stream and therefore is adapted to move control valve 30 to a more open position and when the analyzer 26 detects a decrease in water content to cause valve 30 to move to a more closed position. It should be understood that analyzers 22 and 26 and the associated control valve 30 can each be singularly utilized in the system with the exclusion of the other analyzer. A moisture analyzer 28 can be connected to a heating means of the methanol reconcentration unit 18 and to the conduit 6 for detecting the water content of the water-methanol stream discharging from the unit 18 into line 6. If the water content of the stream changes from a preselected value, such as 5 percent for example, the analyzer 28 delivers a signal through line 36 to the heating means to regulate and change the temperature of the unit 18. Increased water content above the set point causes the temperature of the unit 18 to be lowered thereby decreasing the water in the stream passing through line 6 and, conversely, water content below the set point causes the temperature of the unit 18 to be raised. As stated above, the signals delivered can be electrical or fluid signals but it is preferred that the signals be electrical.

By utilizing this invention in the gas-treating system shown in the drawing, the amount of methanol utilized and the labor requirements were decreased. By heating the injection methanol to vaporize said methanol, an undesired additional small heat load was placed on the system. However, the benefits of this greatly improved mixing, with the result of substantially no formation of solid gas hydrates and ice, and decrease in methanol requirements, greatly increase the overall efficiency of the system. The following is an example of a typical operation such as shown in the drawing.

Typical Operation Feed Gas (2):

Pressure. p.s.i.g. 580 Temperature, F. 70 Flow Rate, MMSCF/D Composition, mol

Nitrogen, CO etc. 5.5 Methane 86.7 Ethane and heavier 7.8 Water, NoJMMSCF l8.5 Methanol Vapor (6):

Presure, p.s.i.g. 595 Temperature, "F. 350 Flow rate (measured as liquid gaL/min. l0 Composition, vol

Methanol 98 Water 2 First Separator (12):

Pressure, p.s.i.g. 570 Temperature, F. l 25 Water in dry gas, ppm. 0.2

Methanol in dry gas, p.p.m 4

Million std cu. ft. per day Liquid methanol injection requires about l2 to l5 gallons per minute of 98% methanol and improper mixing still can cause solid gas hydrates to form, particularly in the heat exchanger.

Parts per million by weight.

Other modifications and alterations of this invention will become apparent to those skilled in the art from the foregoing discussion and accompanying drawing, and it should be understood that this invention is not to be unduly limited thereto.

What is claimed is: 1. An improved method for preventing hydrate and ice formation in a hydrocarbon gas stream by injecting methanol in the said hydrocarbon gas stream and forming a composite hydrocarbon gas-methanol stream, the improvement comprismg:

heating the methanol in a vaporizing zone to a temperature sufficient to vaporize said methanol and maintain said methanol in a vapor phase during injection of said methanol into the gas stream; 7

analyzing the hydrocarbon gas stream at a position upstream of the location at which the methanol is injected to determine the dewpoint of the hydrocarbon gas stream, and establishing a first signal representative of the measured dewpoint; lowering the temperature of the composite hydrocarbon gas and methanol stream in a temperature lowering zone; separating a methanol and water stream from the composite 5 hydrocarbon gas and methanol stream at a location downstream of the temperature lowering zone;

analyzing the water content of the separated methanol and water stream, and establishing a second signal representative of the water analysis; and

controlling the rate of the methanol injected in response to said first signal modified by said second signal.

2. A method, as set forth in claim 1, further including separating a methanol and water stream from the composite hydrocarbon gas and methanol stream at a location downstream from the methanol injection location;

adding makeup methanol to the methanol and water stream; heating the separated methanol and water stream in a methanol reconcentration zone for the removal of water from said separated stream;

analyzing the water content of the heated separated methanol and water stream at a location downstream of the reconcentration zone, and establishing a control signal representative of the water analysis of the heated, separated methanol and water stream;

controlling the temperature to which said separated water and methanol stream is heated in response to said control signal; and

recycling the separated methanol to said vaporizing zone for heating and injecting said stream into the hydrocarbon gas stream. 3. A method, as set forth in claim 1, further including UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,6h4,l 7 February 22, 1972 Merlin 0. Clark It is certified that error appears in the above-identified patent and that 8 Letters Patent are hereby corrected as shown below:

Patent claim 3, column 4, line 35 (original claim 12 (twice amended) line-1+ after "stream" should be inserted through a glycol wash colunn A, line 35, at end of line delete "and"; v colunn h, between lines 35 and 36 should be inserted: separating the methanol from the methanol-containing stream;

and

Signed and sealed this 27th day of June 1972.

(SEAL) Attest:

. ROBERT GOTTSCHALK Commissioner of Patents EDWARD M.FLETCHER,JR. Attesting Officer" 

2. A method, as set forth in claim 1, further including separating a methanol and water stream from the composite hydrocarbon gas and methanol stream at a location downstream from the methanol injection location; adding makeup methanol to the methanol and water stream; heating the separated methanol and water stream in a methanol reconcentration zone for the removal of water from said separated stream; analyzing the water content of the heated separated methanol and water stream at a location downstream of the reconcentration zone, and establishing a control signal representative of the water analysis of the heated, separated methanol and water stream; controlling the temperature to which said separated water and methanol stream is heated in response to said control signal; and recycling the separated methanol to said vaporizing zone for heating and injecting said stream into the hydrocarbon gas stream.
 3. A method, as set forth in claim 1, further including passing the hydrocarbon gas and methanol stream into a demethanizer; separating a methanol-containing stream therefrom; passing the separated methanol-containing stream; and recycling the separated methanol back to the vaporizing zone for heating and injecting the separated methanol into the hydrocarbon gas stream.
 4. A method, as set forth in claim 1, further including dividing the heated methanol stream into a plurality of heated streams and injecting said plurality of methanol streams into the gas conduit at spaced-apart locations relative one to another. 